Design of a sensorized guiding catheter for in situ laser fenestration of endovascular stent

Figures & data

Figure 1. Targeting of the stent graft fenestration site (highlighted with a yellow circle) during an EVAR procedure. Two coordinate systems are represented: a global system (XYZ) in red and a local system (xyz) related to the guiding catheter body in black. Precise targeting requires proper catheter positioning along the longitudinal direction (Z axis), rotation around the catheter main axis (z axis), and bending of the catheter tip (in the yz plane).

Figure 2. Example of a guiding catheter structure made of three different layers. The reinforcement layer is comprised of a braided mesh characterized by a braid angle that changes the flexibility and torque response of the catheter.

Table 1. Target rigidity values for guiding catheters.

Rigidity	Reference Values
Flexural	100–945 10^−6 (N m^2)
Torsional	≥1400 10^−6 (N m^2)
Axial	≥450 (N)

Figure 3. Proposed design solutions for catheter stabilization: (a) ‘Piton-like’ catheter employing a stiff guidewire as a ‘stabilizer’; and (b) a design based on a preformed shape of the catheter body to increase the contact area between the catheter and the graft.

Figure 4. Proposed design solutions for catheter tip bending: (a) a passive solution with a pre-shaped tip and (b) an active solution with a steerable tip.

Figure 5. Possible configuration of sensors. Sensor 1 and 2 are positioned according to the method proposed in [11]. Moreover, Sensor 3 is integrated into the catheter tip as a precautionary measure to refine catheter calibration.

Figure 6. Preliminary prototypes of the four design solutions to test the stabilization and bending systems. Two pictures are reported for each prototype: a global view of the catheter on the left and a zoom detail of the catheter distal part on the right. The two steerable catheters (Designs A and C) have a handle to actively control bending of the tip.

Figure 7. In vitro set-up. A global view of the aorta simulator is shown on the left and a zoom detail showing the plastic tube inserted into the aorta mannequin to simulate the stent graft is shown on the right. Two metal rings are used to indicate the target fenestration sites aligned to the simulated renal ostia (highlighted with blue dotted circles). Note that the plastic tube has no holes at the metal rings.

Table 2. Likert Questionnaire: design solution evaluation. For each item, median values with interquartile range (IQR) (25th; 75th) relative to the four proposed design solutions are reported.

		Low experience		Medium experience		Expert group		Overall
Items	Design	Median (IQR)	p	Median (IQR)	p	Median (IQR)	p	Median (IQR)	p
1. The catheter can be	A	4.00 (3.75;4.00)	0.059	4.00 (4.00;4.25)	0.046	4.00 (4.00;4.50)	0.083	4.00 (4.00;4.00)	0.001
easily advanced	B	4.00 (3.00;4.00)	0.102	4.00 (4.00;4.25)	0.046	4.00 (4.00;4.00)	0.083	4.00 (4.00;4.00)	0.002
	C	3.50 (2.75;4.00)	0.414	3.50 (3.00;4.25)	0.157	2.00 (2.00;2.50)	0.157	3.00 (2.50;4.00)	0.527
	D	2.50 (2.00;3.25)	0.414	3.00 (3.00;3.50)	0.317	2.00 (2.00;2.50)	0.157	3.00 (2.00;3.00)	0.317
2. The catheter can be	A	3.00 (2.00;4.00)	1.000	4.00 (4.00;4.00)	0.046	4.00 (3.50;4.00)	0.157	4.00 (3.00;4.00)	0.083
easily rotated	B	4.00 (3.00;4.00)	0.102	4.00 (3.75;4.00)	0.083	3.00 (3.00;3.50)	0.317	4.00 (3.00;4.00)	0.011
	C	2.00 (2.00;3.00)	0.102	250 (2.00;3.50)	0.564	2.00 (2.00;2.00)	0.083	2.00 (2.00;3.00)	0.021
	D	2.00 (2.00;2.25)	0.059	3.50 (2.75;4.00)	0.564	2.00 (2.00;2.00)	0.083	2.00 (2.00;3.00)	0.052
3. The catheter tip can be	A	4.00 (3.75;4.00)	0.014	4.00 (3.75;4.25)	0.083	4.00 (3.50;4.00)	0.157	4.00 (3.50;4.00)	0.001
properly guided and	B	3.50 (2.75;4.00)	0.414	3.00 (2.75;3.25)	1.000	3.00 (2.50;3.50)	1.000	3.00 (2.50;4.00)	0.527
aligned to the targets	C	2.50 (2.00;3.25)	0.414	4.00 (2.75;5.00)	0.564	3.00 (2.50;3.50)	1.000	3.00 (2.00;4.00)	0.763
	D	2.50 (2.00;3.00)	0.180	2.50 (2.00;3.25)	0.564	2.00 (2.00;2.50)	0.157	2.00 (2.00;3.00)	0.058
4. The catheter can be	A	4.00 (3.00;4.00)	0.025	4.50 (3.75;5.00)	0.083	4.00 (3.50;4.50)	0.157	4.00 (3.00;4.00)	0.002
maintained in a stable	B	3.00 (2.00;4.00)	1.000	2.50 (2.00;3.00)	0.157	4.00(3.00;4.00)	0.564	3.00 (2.00;4.00)	0.763
position during fenestration	C	3.00 (3.00;4.00)	0.317	4.00 (3.00;5.00)	0.157	3.00 (2.50;3.50)	0.317	3.00 (3.00;4.00)	0.059
	D	2.50 (2.00;3.25)	0.414	2.50 (1.75;3.25)	0.564	2.00 (2.00;2.50)	0.157	2.00 (2.00;3.00)	0.132
5. It is possible to reach	A	3.00 (2.00;4.00)	1.000	2.00 (2.00;2.25)	0.083	2.00 (2.00;2.50)	0.157	2.00 (2.00;3.50)	0.166
both targets without	B	2.00 (2.00;3.25)	0.257	2.00 (2.00;2.25)	0.083	2.00 (2.00;3.00)	0.564	2.00 (2.00;3.00)	0.052
changing catheter access	C	2.00 (2.00;3.00)	0.102	2.00 (1.75;2.75)	0.317	3.00 (3.00;3.50)	0.317	2.00 (2.00;3.00)	0.132
	D	2.00 (2.00;2.25)	0.014	2.00 (1.75;2.50)	0.317	3.00 (2.50;3.00)	0.317	2.00 (2.00;3.00)	0.007
6. After the fenestration	A	4.00 (3.00;4.25)	0.102	4.00 (3.75;4.25)	0.083	3.00 (3.00;3.50)	0.317	4.00 (3.00;4.00)	0.011
procedure, the catheter can	B	3.00 (2.75;4.00)	0.655	3.00 (2.75;3.25)	1.000	3.00 (2.50;3.50)	1.000	3.00 (2.50;4.00)	0.739
also be used for cannulation of the renal	C	2.00 (1.75;2.25)	0.059	3.50 (2.00;5.00)	1.000	3.00 (3.00;3.50)	0.317	2.00 (2.00;3.50)	0.248
arteries	D	2.00 (2.00;2.25)	0.014	2.50 (2.00;3.25)	0.564	3.00 (3.00;3.50)	0.317	2.00 (2.00;3.00)	0.058

Bold indicates statistically significant results (p < 0.05).

Table 3. Likert Questionnaire: general evaluation of stabilization and bending. Median values with interquartile range (IQR) (25th; 75th) are reported.

	Low experience		Medium experience		Expert group		Overall
Items	Median (IQR)	p	Median (IQR)	p	Median (IQR)	p	Median (IQR)	p
7. The use of a ‘stabilizer’ allows stable positioning	4.00 (3.75;4.25)	0.014	4.00 (3.75;4.25)	0.083	4.00 (3.50;4.00)	0.157	4.00 (3.50;4.00)	0.001
8. A pre-shaped catheter body allows stable positioning	3.00 (2.75;4.25)	0.655	3.50 (3.50;4.25)	0.157	2.00 (1.50;2.50)	0.157	3.00 (2.50;4.00)	0.739
9. Active bending of the catheter tip is useful to easily reach the fenestration target	4.00 (4.00;5.00)	0.005	4.50 (3.75;5.00)	0.083	4.00 (3.50;4.00)	0.157	4.00 (4.00;5.00)	0.000

Figure 8. Possible cross-sectional views ('A₁-A₁, ' 'A₂-A₂, ' and 'B-B') at positions A₁, A₂, and B, of a design A catheter. Four lumens are shown: a central operative lumen (I) for the guidewire tipped laser fiber and the 'stabilizer', two lumens for EM sensors (II), and a lumen for the steering cable (III). The cross section A₁-A₁ is constant in the catheter blue portion. Then, after the side hole for the 'stabilizer, ' tapering of the central operative lumen (I) as well as the catheter external diameter was started. Two coordinate systems (X_AY_AZ and X_BY_BZ, respectively) used for calculation of the second moment of area (I_xx, I_yy, J_zz) at 'A₁-A₁' and 'B-B' are represented.

Table 4. Mechanical simulations for two different solutions.

	Solution 1			Solution 2
	Section A1	Section A2	Section B	Section A1	Section A2	Section B
Inner Layer
Ixx (mm^4)	2.03	2.03	2.26	2.03	2.03	2.26
Iyy (mm^4)	1.49	1.49	2.14	1.49	1.49	2.14
Jzz (mm^4)	3.52	3.52	4.40	3.52	3.52	4.40
Area (mm^2)	2.58	2.58	4.28	2.58	2.58	4.28
Material	PTFE^®	PTFE^®	PTFE^®	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)
Reinforcement layer
Thickness (mm)	0.05	0.05	0.05	0.05	0.05	0.05
Braiding Parameter	0.02 mm rd, 24 BW, BA = 50°	0.02 mm rd, 24 BW, BA = 60°	0.02 mm rd, 24 BW, BA = 65°	0.02 mm rd, 24 BW, BA = 50°	0.02 mm rd, 24 BW, BA = 60°	0.02 mm rd, 24 BW, BA = 65°
Material	AISI 304V	AISI 304V	AISI 304V	AISI 304V	AISI 304V	AISI 304V
	Pebax^® 3335 (35D)	Pebax^® 3335 (35D)	Pebax^® 3335 (35D)	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)
Outer layer
Thickness (mm)	0.05	0.05	0.01	0.05	0.05	0.01
Material	Pebax^® 3335 (35D)	Pebax^® 3335 (35D)	Pebax^® 3335 (35D)	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)	Pellethane^® 2363 (55D)
EIxx x-axis (N m^2)	867 10^−6	846 10^−6	910 10^−6	760 10^−6	694 10^−6	603 10^−6
EIyy y-axis (N m^2)	653 10^−6	632 10^−6	863 10^−6	693 10^−6	625 10^−6	590 10^−6
EA (N)	1015	991	1 587	890	811	1051
GJzz (N m^2)	2118 10^−6	2112 10^−6	1615 10^−6	1986 10^−6	1995 10^−6	1435 10^−6

CathCAD simulations were performed using mil (a thousandth of an inch) as the unit measure for thickness. Lengths reported in the table are converted to mm and have an approximation by defect. The following abbreviations are used: 0.02 mm rd = round wires 0.02 mm in diameter; BW = number of braiding wires; BA = braiding angle.

Condino S, Ferrari V, Freschi C, et al. Electromagnetic navigation platform for endovascular surgery: how to develop sensorized catheters and guidewires. Int J Med Robot Comput Assist Surg. 2012;8:300–310.

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